1. Technical Field
The invention relates to a power conversion apparatus. Particularly, the invention relates to an over temperature protection mechanism of a power conversion apparatus.
2. Related Art
Referring to FIG. 1, FIG. 1 is a circuit diagram of a conventional power conversion apparatus 100. The power conversion apparatus 100 generates a control signal CTRL through a driver 100 according to a pulse width modulation (PWM) signal PWM. The control signal CTRL is transmitted to a gate of a power transistor PM to turn on and turn off the power transistor PM. Based on the periodic turn on and turn off operations of the power transistor PM, the power conversion apparatus 100 can convert an input voltage to generate an output voltage.
To prevent the power transistor PM or other devices that are liable to produce a high temperature from being damaged due to a high temperature, a thermal resistor RNTC can be configured beside the device to be protected, and the conventional power conversion apparatus 100 has a temperature detection circuit composed of the thermal resistor RNTC, a comparator CMP1 and a current source I1. The current source I1 provides a current to flow through the thermal resistor RNTC, and a voltage is accordingly generated at a connection terminal of the thermal resistor RNTC and the comparator CMP1. The comparator CMP1 compares the voltage and a predetermined threshold voltage Vref to determined whether an environment temperature is excessively high, so as to generate an over temperature protection signal OTP.
In case that the power conversion apparatus 100 is integrated into a chip, the power transistor PM and the thermal resistor RNTC are generally configured at external of the chip. Therefore, the conventional power conversion apparatus 100 requires two independent pins GD and OT to respectively connect the power transistor PM and the thermal resistor RNTC. In this way, a chip area is increased to increase the product cost.